Ultra-low Dielectric Constant Sioch Film And Diffusion Barrier Layer Interaction

With the shrinking in device feature sizes, the integrated circuits (ICs) are moving toward higher performances and giant scale direction. This lead to a rapid increasement of the resistance-capacitance (RC) delay of interconnect, which seriously limits the development of IC. Applying Cu/low dielectric constant (low-k) dielectric to replace the Al/SiO2 in interconnect is one of the most effective approaches. The international technology roadmap for semiconductors (ITRS) projected that (2007), by 2016 the dielectric constant of bulk material used in interconnect of 22 nm IC will be low as 1.9-2.3, which falls into the range of ultra low dielectric constant (ULK). At the present time, the obtained ULK materials are, however, far from application in IC fabrication, because multiple performances of current ULK materials, such as mechanical strength and adhesion, fail to meet the requirements by the back end of line (BEOL) integration technology. Under this background, the thesis firstly explores the preparation of ULK film, then carry out a research on the copper diffusion barrier layer and its reaction with the ULK film. The concrete contents include following aspects:1. An ULK (k=2.41)molecular-pore bridged SiOCH film, i. e., MPB-SiOCH film is prepared using 2,4,6,8-tetrarinyl-2,4,6,8-tetramethylcyclotet-rasiloxane (TVTMCTS) by means of modified spin-on deposition, followed by the UV irradiation. The as-prepared film has Si,0, C contents of 23.5%,43.9%和33.6%, respectively, and a Young's modulus of 5.6 GPa, and a leakage current density of 9.86×10-7 A/cm2 @1 MV/cm. The analysis on the bonding status of film discloses that the as-prepared MPB-SiOCH film contains lots of Si-0-Si ring linkage, C-C bridged linkage and tertiary butyl besides certain amounts of (CH3)3SiO12 2 (M, mono-0-substituted),(CH3)2SiO2/2 (D,di-O-substituted) and (CH3),SiO32 (T, tri-O-substituted) type building blocks, Si-O-C or Si-O-Si cage linkage, as well as Si-O-C ring linkage. In the MPB-SiOCH film, the main chemical environments around the Si atoms are O-Si-C3,O2-Si-C2,O3-Si-C and Si-O4, those around C atoms areC(Si)4,-C-Si3,-C-Si2,-C-Si,C-C/C- and C-0, and those around 0 atoms are 0-Si and O-C. Among these structures,O3-Si-C and Si-O4 show obvious effects on enhancement of MPB-SiOCH film mechanical properties, while the increase in contents of O-Si-C3 and O2-Si-C2 structures are more helpful to k reduction compared with O3-SiO-C.300℃annealing make a further deceases in MPB-SiOCH film's k value (k=1.94) and leakage current density (2.96×10-7 A/cm2 @1 MV/cm), and 300℃annealed MPB-SiOCH film shows a strong capability of anti moisture uptake. There is no big variation observed in FTIR spectrum between 300 and 400℃annealed MPB-SiOCH film, indicating a relative good film thermal stability. Generally, after the comprehensive evaluation on film's performance, preparation technology and integration capability etc, there exhibits a bright future for the MPB-SiOCH film to be developed and appllied in IC interconnect.2. The influences of Hf contents in WHfN films on the films' resistivity, thermal stability and Cu diffusion barrier capabilities are investigated. The experimental results show that, the resistivity of WHfN film is increased with the increase of Hf content, while lowering the N2/Ar flow ratio is helpful for gaining WHfN film whose resistivity is≤500μΩ. cm. As the N2/Ar flow ratio is 1:14, The thermal stability of the resultant WHfN film is increased, (> 600℃). At the same time, the increase of the content of Hf in WHfN film (W/Hf atomic ratio is in the range of 1:0.07～1:0.33) enhances the film's barrier performance. The analysis on films's bonding configuration shows that, in comparison with WN, the WHfN film contains W-W-Hf, W-N-Hf, Hf-N, W-Hf-N bonds, besides metallic W-W and W-N. Among these bonding structures, the formation and added concentration of W-N-Hf are more helpful for enhancing the film's barrier performance. It is found, on Si substrate, the failure temperature of WHfN(10nm) film to prevent Cu from diffusion is 750℃, and WHfN(10nm) film obviously exhibits a better barrier performance than WN(10nm) film deposited under the equal condition. Further, The barrier performance of Ru(5nm)/WHfN(5nm)double layer barrier film on Si substrate is studied. The experimental result show that, the failure temperature of the Ru(5nm)/WHfN(5nm) barrier film is as high as 700℃, and this double layer barrier film also exhibits a distinct enhancement in barrier performance compared with whatever Ru(10nm) or Ru(5nm)/WN(5nm) barrier films, which are deposited under the equal condition. 3. The investigation on the interaction between MPB-SiOCH film (K=1.94) and Ru(5nm)/WHfN(5nm) double layer barrier film is carried out. Firstly, by using XPS analysis, the interfacial bonding characteristic of WHfN/MPB-SiOCH sample and that of WHfN/MPB-SiOCH sample are comparatively studied. The experimental data show that, compared with the interface of WN/MPB-SiOCH sample, the interface of WHfN/MPB-SiOCH sample forms quantity of N-Hf-0,Hf-O-Si and possible small amount of W-O-Hf bonding structures, besides the 0-W. This make the bond density and strength of the WHfN/MPB-SiOCH interface enhanced enormously, compared to those of WN/MPB-SiOCH interface, suggesting a greatly improved adhesion for the WHfN/MPB-SiOCH interface, which benefits reliability of interconnect. Further, using Ru(5nm)/WHfN(5nm) as the barrier film, the the thermal stability of Cu/Barrier/MPB-SiOCH/Si stacked system is investigated. The experimental results show that, after annealing at 450℃(N2 atmosphere) for 45 min, there is no Cu diffusion observed in the system, at the same time, the films stacked in the system adhere with each other well and there is no found delamination phenomena.4. Using ZrCl4 or HfCl4 and NH3 as the precursors, the initial surface reactions between atomic layer deposition (ALD) ZrN or HfN barrier layer and ULK SiOCH film are studied by ab initio computational method. All the calculation works are carried out using quantum chemistry calculation and under the framework of B3LYP hybrid density functional, which corresponds to the Becke's three parameter exchange functional (B3) along with the Lee-Yang-Parr gradient-corrected correlation functional (LYP). It is showed that, ZrCl4 are hardly absorbed on the -CH3 and -OCH3 terminated surface of SiOCH film, while can chemisorp on the -OH and -NH2 terminated film surface much easily. The variation between SiOCH film backbones can lead to a difference, at most, of reactive energy by 9.15 kcal/mol, which is related to the dative effect between Zr and backbone 0 atoms during the reaction transition state. The reaction of NH3 with the metalized surface by Zr is exothermic, therefore raising the deposition temperature properly will benefit the preparation of ALD ZrN film. The product of Si-O-ZrCl2-NH2. is more stable than Si-NH-ZrCl2-NH2, therefore, pretreatment to form-OH rather than-NH2 terminated surface might more in favor of the growth of ALD ZrN film. The reaction mechanism and reaction related values for ALD HfN barrier film growing on the SiOCH film surface are similar to those of ALD ZrN film.